This invention is in the field of iminodiacetonitrile (IDAN) preparation. More particularly it is directed to a process for preparing IDAN by reacting hexamethylenetetramine, formaldehyde, and HCN in an aqueous reaction medium (an aqueous reaction mixture). Even more specifically, this invention is directed to a continuous process in which said aqueous reaction mixture is passed through a continuous reaction zone (e.g., a tubular reactor, a continuous overflow autoclave, or the like) to form IDAN.
It was reported over 80 years ago that IDAN is obtained in an unspecified yield by reacting hydrogen cyanide with HMTA. Eschweiler, Ann., 278, 229-239, (1894). Later, in 1921, Dubsky et al, Ber., 54, 2659, confirmed that IDAN can be formed by reacting HMTA with aqueous hydrogen cyanide. In 1957, in U.S. Pat. No. 2,794,044, Miller disclosed the preparation of IDAN in a yield of about 65% by reacting ammonia, formaldehyde and hydrogen cyanide in an aqueous acid solution having a pH of 5.5 to 6.5. More recently, in U.S. Pat. No. 3,167,580, Saunders et al showed in examples that IDAN is obtained rapidly in a continuous process comprising bringing into reactive contact acid stabilized formaldehyde and hydrogen cyanide mixture and ammonia under carefully controlled reactant ratios and temperatures and at a pH of greater than 7 using a continuous reaction zone (a tubular reactor).
Stutts, U.S. Pat. No. 3,412,137, teaches a process for preparing IDAN by reacting an aqueous solution of HMTA and HCN in an aqueous medium buffered at a pH of about 5-6.5
Philbrook et al, U.S. Pat. No. 3,886,198, teach a process for preparing IDAN which comprises forming an aqueous mixture of HMTA, HCN, and a strong acid and continuously passing said mixture (which has an acidic pH -- e.g., a pH of 3-5) through a tubular reactor at about 50.degree.-120.degree. C to form the desired IDAN.
Sexton, U.S. Pat. No. 2,895,989, teaches the conversion of IDAN to an alkali metal salt of iminodiacetic acid (i.e., to IDAM) by hydrolyzing the IDAN with an alkali metal hydroxide. Sexton also teaches the conversion of such salt to iminodiacetic acid (IDA).